Oftentimes in surgical procedures a powered surgical instrument such as a drill, saw, reamer, or the like, is used on a bone of a patient. As such, a surgeon may be tasked with determining, based on feel alone, when the instrument passes through the bone of the patient. Furthermore, once the instrument has been passed through the bone of the patient, it may be desirable to provide a measure of the displacement of the leading edge of the instrument relative to a reference point when the leading edges passes from a first medium having a first density to a second medium having a second density (e.g., when the leading edge of the surgical instrument passes completely through the bone). Traditional approaches of determining such displacements may require removal of the instrument from the bone and/or use of a separate depth gauge tool.
One particular context in which determining the displacement of an instrument passing through a bone is important is in the context of drilling holes in bone for placement of screws, pins, or the like. Following traumatic injury, plate and screw placement relative to a bone may be critical for adequate repair. As such, inadequate and inaccurate depth measurement following orthopedic drilling procedures may result in incorrect screw lengths, which can lead to surgical complications such as device instability, damage to anatomic structures, or device failure. Furthermore, placement of pins (e.g., transcutaneous pins) may require accurate placement of the distal end of the pin relative to a bone structure (e.g., into a hard outer cortex of the bone).
Another context in which determining when an instrument passes from a first medium to a second medium is advantageous concerns determining completion of an operation using an instrument. For example, whether sawing, drilling, reaming, or performing some other powered operation relative to bone, upon the completion of the operation (i.e., upon passing completely through the bone or into a specific layer of the bone), the operation is preferably arrested to prevent damage to surrounding tissue by the powered instrument. Currently such termination of the operation largely is the responsibility of a surgeon using feel alone to determine an operation has completed.
However, determining when an instrument passes through a bone may be complicated because of the anatomical structure of the bone. For instance, as shown in FIGS. 1A, 1B, and 1C, the bony structure of the human anatomy consists mainly of cortical bone 10 having a hard outer cortex 12 and a soft inner medullary layer 14. As described above, oftentimes powered instruments are used in relation to the bone, which, given the hard nature of bone, may be difficult to operate on using hand operated tools. With the ease of powered instruments also comes difficulty in terminating operation of the instrument once the operation on the bone has been terminated and/or determining a depth of an operation relative to a bone.
For example, as shown in FIG. 1A, when using a rotating drill bit 16 to form a bicortical bore 18 through the cortical bone 10, the rotating drill bit 16 passes through a first portion 12a of the hard outer cortex 12, a soft non-resistant medullary layer 14, and a second portion 12b of the hard outer cortex 12. However, as shown in FIG. 1B, when using a rotating drill bit 16 to form a unicortical bore 20 through the cortical bone 10, the rotating drill bit 16 passes through an entry point 22a of the hard outer cortex 12 and an exit point 22b of the hard outer cortex 12 a first portion 12a without penetrating the soft non-resistant medullary layer 14. Furthermore, in FIG. 1C, an instrument (e.g., a saw blade 130 having a blade edge 132) may pass through the entirety of the bone. As such, the saw blade edge 132 may pass through a first portion 134 of the bone 10 comprising only a first portion 12a of the hard outer cortex 12, a second portion 136 of the bone 10 comprising both hard outer cortex 12 and the soft medullary layer 14, and a third portion 138 of the bone 10 comprising only of a second portion 12b of the hard outer cortex 12. In this regard, each of the first portion 134, second portion 136, and the third portion 138 may have interfaces at which the perceived density of the medium changes. Further still, each of the portions 134, 136, and 138 may exhibit substantially the same density as the hard outer cortex 12 may be subjected to the instrument in all portions. Thus, variables such as the relative thickness of the hard outer cortex 12 and soft medullary layer 14, whether the operation is unicortical or bicortical, and/or the relative amount of hard outer cortex 12 and medullary layer 14 subjected to the instrument may affect the ability of the user to sense when the leading edge of the instrument passes through the relative portions of the bone 10. In any regard, in all these examples a surgeon may be required to determine when the drill bit passes through the bone by feel alone. As can be appreciated, in each context described in FIGS. 1A-1C, the feel demonstrated by the instrument may differ. As such, consistently determining a depth of an operation using a powered instrument relative to the bone 10 may be difficult. That is, the determination of when the drill bit has passed through a portion of or the entirety of the bone may require skill by the surgeon and may not be repeatable for all bones of all patients. In the event the surgeon does not cease an operation of the powered instrument upon completion of the operation, surrounding tissue or other structures may be damaged.
As such, a possible resulting complication of an operation using a powered instrument is that the surgeon may not precisely “feel” the instrument pass through a desired portion of the bone, thereby possibly damaging tissue adjacent to the bone or resulting in the instrument not passing into a desired portion of the bone. Another complication may occur if the depth of a bore or cut is not properly measured. For instance, if using a depth gage, the depth gage may be improperly placed or the gage may be grasped prior to passing the distal end of the bore. In either regard, a depth measurement may be determined that is smaller or larger than the true depth. Accordingly, current techniques to operations using powered instruments on a patient may be inefficient, thus adding cost and the potential for adverse complications to the operation.